1. Technical Field of the Invention
The present invention relates to a reduced noise fan stationary blade whose aerodynamic capability is high and in which noise reduction is possible.
2. Description of the Related Art
An engine for a supersonic airliner is a turbo fan engine having a low bypass ratio, and a fan noise is a noise source next to a jet noise. Moreover, in an engine for a subsonic airliner, the bypass ratio has increasingly been raised, and a ratio of the fan noise has relatively increased. Therefore, there has been a demand for further decrease of the existing regulated value of the fan noise in order to raise a future environmental adaptability.
A main source of the fan noise is a tone noise by interference of a moving blade rear flow and stationary blade. Means such as (1) attachment of a sound absorption liner, (2) optimization of the number of moving/stationary blades, and (3) enlargement of a moving/stationary blade interval have heretofore been used as reduction means of the tone noise.
In (1) the attachment of the sound absorption liner, a once generated sound is absorbed by the sound absorption liner. In this means, however, a sound absorption member, for example, of about 70 kg is required for reducing the existing noise by 3 dB, and there is a problem that an engine weight increases.
In (2) the optimization of the number of moving/stationary blades, a cutoff phenomenon is used in which an acoustic mode having a specific frequency propagated in a duct is exponentially attenuated. The number of moving/stationary blades is usually selected so as to cut off a primary peripheral-direction acoustic mode of a blade passing frequency.
However, this means has problems that a method of determining the number of moving/stationary blades is restricted in design, and that the mode capable of being cut off is also limited to a specific mode.
The means of (3) the enlargement of the moving/stationary blade interval enlarges a distance in which the rear flow discharged from a moving blade rear edge reaches the stationary blade, promotes the attenuation of the rear flow, and weakens a nonstationary aerodynamic force on a stationary blade surface as the noise source.
However, this means lengthens an axial length of the entire engine and causes a weight increase.
Moreover, the above-described noise reduction technique has heretofore been applied to the turbo fan engine, and the existing noise regulated value can be achieved, but more noise reduction effect has not been expected.
On the other hand, a sweep lean stationary blade has been reported in the following documents, in which a stacking line of a fan stationary blade is slanted in axial and peripheral directions as shown in FIGS. 1A, 1B in order to achieve the noise reduction of the low bypass ratio turbo fan engine more than is possible today. The figures come from the following two sources:
(1) xe2x80x9cDesign Selection and Analysis of a Swept and Leaned Stator Conceptxe2x80x9d, NASA/TM-1998-208662, December 1998.
(2) xe2x80x9cBenefits of Swept and Leaned Stators for Fan Noise Reductionxe2x80x9d, 37th Aerospace Sciences Meeting and Exhibit, January 1999.
It has been reported that the fan noise is reduced by about 3 EPNdB in these conventional sweep lean stationary blades. This is because the stationary blade is slanted, a phase of interference with the moving blade rear flow as the sound source is diversified in the radius direction, and as a result the acoustic mode of a radius direction is raised in order and cut off. However, the conventional sweep lean stationary blade has a problem that a system loss increases by about 3% with the noise reduction.
That is, for the conventional sweep lean stationary blade, the noise reduction effect is obtained, but there is a problem that an aerodynamic capability is deteriorated.
The present invention has been developed in order to solve the above-described problems. That is, an object of the present invention is to provide a reduced noise fan stationary blade in which total pressure losses of both hub and tip sides are reduced, the noise can be reduced on both the hub and tip sides, and thereby noise reduction can be achieved without deteriorating an aerodynamic capability. As used in this description and in the appended claims, xe2x80x9ctip sidexe2x80x9d means the side of the blade opposite the hub side.
As a result of various capability analyses of a conventional sweep lean stationary blade, the inventors of the present invention have found by the analyses that a lean angle of a fan stationary blade is set in a direction opposite to a rotation direction and a high loss region in the vicinity of a hub is thereby improved. Then, it has been confirmed by the analyses that the lean angle of the direction opposite to the rotation direction is set only in the high loss region in the vicinity of the hub, the lean angle of the rotation direction is set in other regions, and thereby the reduced noise fan stationary blade having an aerodynamic loss suppressed can be realized. The present invention is based on such inventive findings.
That is, according to the present invention, there is provided a reduced noise fan stationary blade which has a negative lean angle xcex8L of a direction opposite to a rotation direction in the vicinity of a hub, and a positive lean angle xcex8L of the rotation direction in other regions on a tip side.
According to the constitution, the total pressure losses of both the hub and tip sides are reduced, and the noise can be reduced on both the hub and tip sides.
According to a preferred embodiment of the present invention, the negative lean angle xcex8L is about xe2x88x9220xc2x0 or more, and less than 0xc2x0 in the high loss region in the vicinity of the hub, and the positive lean angle xcex8L is about 10xc2x0 or more, and less than 40xc2x0 on the tip side.
From study results of the aerodynamic capability described later, it has been confirmed that the total pressure loss is improved and a noise reduction effect is obtained in the range of the lean angle of about xe2x88x9220xc2x0 or more, less than 0xc2x0 on the hub side, and in the range of the lean angle of about 10xc2x0 or more, less than 40xc2x0 on the tip side.
It is preferable that the negative lean angle xcex8L is xe2x88x9210xc2x0xc2x13xc2x0 in the high loss region in the vicinity of the hub, and the positive lean angle xcex8L is 30xc2x0xc2x13xc2x0 on the tip side.
From the study results of the aerodynamic capability, it has been confirmed that the total pressure loss is minimized and the noise reduction effect is obtained at the lean angle of xe2x88x9210xc2x0xc2x13xc2x0 on the hub side, and at the lean angle of 30xc2x0xc2x13xc2x0 on the tip side.
There is further provided a reduced noise fan stationary blade which has a positive sweep angle xcex8s. Since the blade has such positive sweep angle xcex8s, the noise can further be reduced on both the hub and tip sides.
The positive sweep angle xcex8s is about 15xc2x0 or more, and less than 40xc2x0 on the hub side, and is about 0xc2x0 or more, and 200 or less on the tip side.
From the study results of the aerodynamic capability described later, it has been confirmed that the total pressure loss is improved and the noise reduction effect is obtained in the range of the positive sweep angle on the hub side of about 15xc2x0 or more, less than 40xc2x0, and in the range of the angle on the tip side of 0xc2x0 or more, 20xc2x0 or less.
It is preferable that the positive sweep angle xcex8S is 20xc2x0xc2x13xc2x0 on the hub side, and is also 20xc2x0xc2x13xc2x0 on the tip side.
From the study results of the aerodynamic capability, it has been confirmed that the noise reduction effect is maximized and the total pressure loss can be reduced with the sweep angle xcex8s of 20xc2x0xc2x13xc2x0 on the hub side, and the total pressure loss is reduced and the noise reduction effect is obtained with the angle of 20xc2x0xc2x13xc2x0 on the tip side.
Other objects and advantageous characteristics of the present invention will be apparent from the following description with reference to the accompanying drawings.